In order for the black and white sections of the movie to be shot in the same quality as the rest of the film, Kodak produced a limited supply of its Double-X black and white film stock in 70mm. This film stock was chosen specifically for its heritage - it was originally sold to photographers as Super-XX during World War II and was very popular with photojournalists of the era.
Matt Damon was on a break from acting as a promise to his wife, with one condition: it would go on hold if Sir Christopher Nolan called. As luck would have it, Nolan offered Damon the role of Leslie Groves, and the break went on hold.
The Trinity detonation scene uses a combination of practical effects and digital compositing. Multiple explosions were performed practically, with a hybrid of gasoline, propane, aluminium and magnesium substances involving big miniatures. These were filmed at high speeds from multiple angles, and then layered using digital effects to create the iconic mushroom cloud.
Albert Einstein is shown walking in the woods with Kurt Gödel. The two of them did actually take long walks together, as friends at the Institute for Advanced Studies.
The AEC hearing room 2022 scenes were filmed in an existing office room with four walls and no air conditioning. Sir Christopher Nolan wanted the claustrophobia for the actors to be genuine, and set a challenge for filming within limited space without being able to move the ceiling or the walls as normally would be done on a studio set. He and the other crew members had to crouch out of camera range or sit on the floor during filming.